The greenkeeperapp is used on any web browser including phones.
This ppt slide explains the model in a lot of detail. https://turf.unl.edu/PGR%20GDD%20Prov%20RI.pdf Page 4 and 5 have how the clipping yields looks if applied every 4 weeks, 800 GDD, 400 GDD and 200 GDD. Look how it stays in suppression at 200GDD (top left page 6).
The best way to do this is to collect clipping data, but none of us want to do that too.